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Speaker 1: Linda dot com slash brain Stuff. Welcome to brain Stuff
Speaker 1: from how Stuff works dot com where smart Happens. I
Speaker 1: am Marshall Brain with today's question, what makes your knuckles pop?
Speaker 1: If you've ever laced your fingers together, turns your palms
Speaker 1: away from you and bent your fingers back, you know
Speaker 1: what knuckle popping sounds like. Joints produced that crack when
Speaker 1: bubbles burst in the fluids surrounding the joint. Joints are
Speaker 1: a meeting point between two separate bones, held together and
Speaker 1: in place by connective tissues and ligaments. All of the
Speaker 1: joints in our bodies are surrounded by synovial fluid, a thick,
Speaker 1: clear liquid. When you stretch or bend your finger to
Speaker 1: pop the knuckle, you're causing the bones of the joint
Speaker 1: to pull apart. As they do this, the connective tissue
Speaker 1: capsule that surrounds the joint is stretched. By stretching this capsule,
Speaker 1: you increase its volume, and, as we know from chemistry class,
Speaker 1: with an increase in volume comes a decrease in pressure.
Speaker 1: So as the pressure of the synovial fluid drops, gas
Speaker 1: is dissolved in the fluid become less soluble, forming bubbles
Speaker 1: through a process called cavitation. When the joint is stretched
Speaker 1: far enough, the pressure in the capsule drops so low
Speaker 1: that these bubbles burst, producing the pop that we associate
Speaker 1: with knuckle cracking. It takes about five to thirty minutes
Speaker 1: for the gas to redissolve into the joint fluid. During
Speaker 1: this period of time, your knuckles won't crack again. Once
Speaker 1: the gas is dissolved, cavitation is once again possible, and
Speaker 1: you can start popping your knuckles again. As for the
Speaker 1: harms associated with this habit, according to Anatomy and Physiology
Speaker 1: Instructors Cooperative, only one in depth study regarding the possible
Speaker 1: detriments of knuckle popping has been published. This study, done
Speaker 1: by Raymond Broder and published in the Journal of Manipulative
Speaker 1: and Physiological Therapeutics, examine three hundred knuckle crackers for evidence
Speaker 1: of joint damage. The results revealed no apparent connection between
Speaker 1: joint cracking and arthritis. However, habitual knuckle poppers did show
Speaker 1: signs of other types of damage, including soft tissue damage
Speaker 1: to the joint capsule and a decrease in grip strength.
Speaker 1: This damage is most likely a result of the rapid,
Speaker 1: repeated stretching of the ligaments around the joint. On the
Speaker 1: positive side, there's evidence of increased mobility and joints right
Speaker 1: after popping. When joints are manipulated, the gold g tendon organs,
Speaker 1: a set of nerve endings involved in humans motions, sense
Speaker 1: are stimulated and the muscles surrounding the join to relax.
Speaker 1: This is part of the reason why people can feel
Speaker 1: loose and invigorated after leaving a chiropractor's office where a
Speaker 1: cavitation is induced as part of the treatment. Backs, knees, elbows,
Speaker 1: and all other movable joints are subject to the same
Speaker 1: kind of manipulation as knuckles are. Do you have any
Speaker 1: ideas or suggestions for this podcast? If so, please send
Speaker 1: me an email at podcast at how stuff Works dot com.
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